(a) Field of the Invention
An exemplary embodiment of the present invention relates to the fuel cell stack of a fuel cell system and more particularly, to a separation plate having a micropore body structure and a fuel cell including the same.
(b) Description of the Related Art
Generally, a fuel cell includes unit cells that generate electrical energy through an electrochemical reaction of hydrogen and oxygen. The fuel cell includes separation plates with a membrane-electrode assembly (MEA) interposed therebetween. The separation plate includes a reaction flow channel that supplies a reaction gas, including fuel and air, to a membrane-electrode assembly, and a cooling flow channel through which a coolant flows. A gas diffusion layer that diffuses the reaction gas is formed on both surfaces of the membrane-electrode assembly.
Maximization of the performance of the fuel cell, requires the interval between the reaction flow channels of the separation plates to be dense to provide a uniform surface pressure and a constant permeability across a reaction front of the gas diffusion layers and the membrane-electrode assemblies. A reduction of the interval between the reaction flow channels of the separation plates to prevent various failures occurring in a process of forming the separation plate is limited. Consequently, the following performance deteriorate factors of the fuel cell may result.
For example, a substantial interval between the reaction flow channels, causes stress to become concentrated on a land surface where the separation plate and the gas diffusion layer are positioned adjacent to each other. In particular, the compromised porous structure of the gas diffusion layer reduces the permeability of a reaction gas and the diffusion performance of a reaction gas and exhaust performance of generated water deteriorates. Furthermore, a surface of the reaction flow channel has low stress and the gas diffusion layer protrudes toward the flow channel unit of the separation plate. In other words, the viscosity of a fluid may deteriorate.
Further, the structure of the gas diffusion layer is damaged by the land unit of the separation plate since the carbon fibers penetrate the electrode layer of the membrane-electrode assembly in a broken component, thereby damaging the electrode layer. Still further, a chemical reaction is active because a reaction gas continuously supplied to the flow channel unit within the flow channel unit in which the gas diffusion layer is exposed. However, contact resistance increases due to insufficient surface pressure between the gas diffusion layer and the membrane-electrode assembly. Namely, the electrons generated by a reaction may encounter decreased mobility.
Typically, a molded porous body including porous structures that includes fine apertures and a three-dimensional porous structure that include channels is formed in a metal thin plate. Furthermore, a method of inserting a micropore structure capable of uniformly distributing surface pressure and improving the diffusion of a reaction gas and exhaust performance of generated water is used instead of the separation plate including the reaction flow channel For example, the micropore structure, includes a metal foam or wire mesh, has a high open ratio and functions as a surface pressure distribution structure to uniformly compress the gas diffusion layer. The metal foam includes many interconnected bubbles within metal materials. Additionally, the metal foam is suitable for a separation plate for a fuel cell material since the metal foam allows a fluid to pass therethrough and has a high surface area ratio per unit volume and increased strength.
However, the metal foam is limited by the entire reaction front cannot be utilized since the internal bubbles are randomly connected and thereby limits the control of a flow of the reaction gas and generated water. Furthermore, the parasitic power of the fuel cell system and the volume of the fuel cell increase since the micropore structure is applied to the separation plate, and thus a difference pressure within the separation plate increases. Furthermore, the operation safety of the fuel cell may be reduced since the micropores are frequently clogged during a supersaturate state within the fuel cell.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.